Colossians 1:16-17 in NWT
Instead of verse 16 reading: "because by means of him all [other] things were created in the heavens and upon the earth,..." they could have written it "because by means of him all things were [not] created in the heavens and upon the earth..."
If Christ were 'created' then by him all things were 'not' created, just most things.
Also instead of verse 16b reading: "All [other] things have been created through him and for him." It could instead read: "All things have [not] been created through him and for him." and verse 17 could read: "Also, he is [not] before all things and by means of him [not] all things were made to exist.
If you can point out that they are not clarifying the Bible but instead negating it by using the word [not] then maybe it will shake them up a bit and put a stone in their shoe.
Matt Slick at CARM.org said he simply asks the JW to read the verses without the inserted word 'other' and finds they can't do it which is very interesting sociologically. In fact, he's not been able to get a single JW to do it for him.
The best strategy for using the Bible with the JW's is to use their own interlinear Greek/English New Testament to show how they've changed the verses but that won't work for the changes in the Old Testament where they've made changes also. If you don't have an interlinear you might want to argue that you don't want to use the NWT because only the Jehovah's Witnesses use it and no other group uses it or trusts it. There are a number of passages you can use effectively that haven't been changed but the ones you'll probably want to use the most are the ones they've changed and you should check those out first in the NWT before going to them.